MIgrated from 6.12.65 to 10.13.66 and now FAX not working


We recently migrated from Freepbx 6.12.65 to 10.13.66. SIP phone calls work fine. However FAX machines are not able to send FAX anymore. I did captures on the old version and the new version and when I compare the packet captures on the two versions the only difference I see is that version 6.12.65 was sending FAX machines IP address in the SDP to the SIP provider. However with the new version 10.13.66 the server is sending its own NATted public IP address as the “connection ID” in the SDP packets for media. I believe this is the reason why its not working. The FAX call connects but then after some time it drops (Freepbx sends a bye). Does anyone know how to make Freepbx not send its own IP address as the connection ID? I checked the SIP server and extension settings and the “can reinvite” option is set to yes.

I have also attached a picture of wireshark showing the comparison of the two versions packet capture. Yellow one is the one working and it sends the FAX machine’s IP address as the connection Information. Red one is the one not working and it sends Freepbx NAT IP in the connection information. I believe this is the issue as this is the only difference I see between the two.

Please let me know how to troubleshoot or resolve this issue.

Thank you.


Any ideas? Any suggestion please?


Can anyone help me with this issue? I have searched many blogs but cannot find the solution to this issue.


It is really strange that the fax negotiation is taking place. It negotiates G711 instead of T38 as our provider does not support T38 and then it just drops without sending the fax. Does anyone has any idea why it is not sending the fax after negotiating everything? Why does it drop the call? I dont see any errors in the cli either…

See the Asterisk log, you’ll probably find answers there…


What log files should I be looking at and what location?


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